Abstract: An electrolytic pre-enrichment of a feed stream to a combined electrolysis nd catalytic exchange ("CECE") heavy water production process. A deuterium enriched liquid or vapour stream from electrolytic cells is applied as a feed to the first stage of a CECE deuterium enrichment process. By deploying a portion of available electrolytic cell capacity in the pre-enrichment stage, advantages are achieved, particularly where available electrical power fluctuates or when a "turned down" CECE process is desired.

Abstract: A gas-liquid contacting apparatus is provided having downcomers which are closed at their lower ends by perforated, inclined, liquid distributing, gas entry retarding, plates. The downcomers each depend from a drainage opening bounded by a weir on a perforated, liquid frothing tray. Alternate trays have central drainage openings and are interposed with trays having drainage openings adjacent opposite tray sides. The trays have liquid frothing perforations across the whole of each tray including the area beneath each drainage opening. The perforations beneath a drainage opening occupy an area per unit area of the drainage opening in the range 0 to 25% less than the perforations per unit area in the remainder of that tray. The apparatus produces a frothing layer on the trays in which the perforated, inclined, liquid distributing, gas entry plates are immersed and, which gives a good liquid flow distribution across the tray so that a high efficiency of contact between the gas and the liquid is achieved.